Recently, blue LED and white LED exhibiting great luminance have been developed, and the application is expanding into areas such as backlights of bulletin boards, full color displays and portable telephones. As the encapsulating material for photoelectric conversion devices such as LED, epoxy resin compositions comprising a compound having epoxy group and a curing agent of an acid anhydride have heretofore been used since the epoxy resin composition exhibits an excellent colorless and transparent property.
As the curing agent for compounds having epoxy resin used for photoelectric conversion devices, alicyclic dicarboxylic acid anhydrides such as methylhexahydrophthalic acid anhydride, norbornanedicarboxylic acid anhydride, methyltetrahydrophthalic acid anhydride, hexahydrophthalic acid anhydride and tetrahydrophthalic acid anhydride are widely used (Patent References 1 to 4). Among these agents, methylhexahydrophthalic acid anhydride and methyltetrahydrophthalic acid anhydride which are liquid at the ordinary temperature are mainly used due to easy handling.
However, when the above alicyclic dicarboxylic acid anhydride is used as the curing agent, it is necessary that a curing accelerator be added to achieve sufficient curing due to the small reactivity of curing.
As the curing accelerator, quaternary phosphonium salts, tertiary amines, imidazoles, organic hydrazides and diazabicycloalkenes are used. However, these curing accelerators have drawbacks in that the curing accelerators are very expensive, the method of the use is complicated, and deterioration in color tone and decrease in the strength arise when the curing accelerators are used in a great amount.    Patent Reference 1: Japanese Patent Application Laid-Open No. 2000-344868    Patent Reference 2: Japanese Patent Application Laid-Open No. 2001-114868    Patent Reference 3: Japanese Patent Application Laid-Open No. 2002-97251    Patent Reference 4: Japanese Patent Application Laid-Open No. 2003-26763